Evaluation of Hypernasality in Vowels Using Voice Low Tone to High Tone Ratio

Objective: The voice low tone to high tone ratio (VLHR) is defined as the power ratio of low frequency to high frequency energy obtained by dividing the voice spectrum with a specific cutoff frequency. In a previous study, VLHR correlated significantly with nasalance and perceptual rating of hypernasality for a single vowel. The methodology was optimized in this study by investigating the correlations among other vowels. Design: Voice signals of six sustained vowels vocalized by subjects with hypernasality were collected. Vowel nasalance was obtained with a nasometer, and hypernasality rating scores were provided by two speech-language pathologists. The VLHRs calculated using different cutoff frequencies were correlated with nasalance and hypernasality rating scores. Participants: Eight subjects with hypernasality caused by palatal fistula or velopharyngeal insufficiency. Main Outcome Measures: VLHR, nasalance, and hypernasality rating score. Results: The correlation of VLHR with nasalance and hypernasality rating was most significant using a cutoff frequency of 600 Hz. The correlation of VLHR with nasalance was significant (r  =  .62, p < .01, Pearson's correlation), as was the correlation of VLHR with hypernasality score (Spearman's rank correlation coefficient  =  .62, p < .01). Conclusions: VLHR correlated significantly with nasalance and hypernasality in the six sustained vowels and may provide another quantitative index for the evaluation of hypernasality in sustained vowels.